The invention relates to an apparatus for playing storage discs which can be set into rotation about a central axis of rotation by a drive motor and which cooperate with an optical unit which during the rotation writes information onto or reads it from an active side, which storage disc can be pressed against a disc platen with the aid of a pressure device, which acts upon one of its disc surfaces in order to be held in its play position and to preclude vibrations of the storage disc itself, the disc platen having a diameter which substantially corresponds to that of the storage disc.
JP-A-09259496 describes an apparatus for playing optical storage discs. The apparatus has a turntable and a clamping disc. The turntable and the clamping disc have diameters corresponding to that of the optical storage disc. The turntable, which is situated underneath the storage disc, is rotationally driven for playing; the turntable receives the optical storage disc and can move this disc upwards against the freely rotatable clamping disc. The side of the storage disc to be provided with or provided with information faces downwards. As a consequence, the optical unit of the apparatus is situated underneath said disc and reads it or inscribes it from underneath. In order to achieve that the laser light, which should pass through the turntable, reaches the storage disc, this turntable consists of a transparent material. Disc vibrations are suppressed between the large-area turntable and clamping disc but the construction is susceptible to soiling.
From JP-A-60 160 059 an apparatus construction is known by means of which natural vibrations of an optical storage disc are to be precluded. For this purpose, a damping disc is placed onto the storage disc during operation. The mechanism used for placement and the required space are not acceptable in the case of compact apparatuses.
It is an object of the invention to provide an apparatus of the type defined in the opening paragraph, which is of simple construction, which is compact and in which vibrations of the storage disc with respect to the optical unit are precluded, particularly when used in a vehicle.
According to the invention said object is achieved by means of an apparatus having the following characteristic features:
a) the pressure device acts only upon the information-free central area of the storage disc,
b) the pressure device, which acts upon the information-free central area of the storage disc is freely rotatable,
c) the disc platen is in frictional engagement with the storage disc when this storage disc is pressed into position and is constructed as a turntable, which can be set into rotation by the drive motor,
d) the disc platen can be brought into contact with the label side of the storage disc.
In such an apparatus the functions have been reversed in comparison with the known apparatuses. The known disc platen, against which the storage disc is pressed in an upward direction, is no longer freely rotatable but converted into the driven turntable. The previously driven turntable of the apparatus is converted into a freely rotatable pressure member and merely serves to press the central part of the storage disc against the disc platen. This function reversal has substantial advantages. The construction requires little space, i.e. it can remain compact; the storage disc cannot vibrate freely and the laser light can reach the storage disc unimpededly, as a result of which the aforementioned soiling cannot occur. These conditions make it particularly suitable for mounting in motor vehicles. The disc platen is applied to the label side of the storage disc with friction. As a consequence, the storage disc is driven from the label side. Since the storage disc is in frictional engagement in the proximity of its periphery no intricate clamping mechanisms are required.
In a further embodiment of the invention the drive motor sets the disc platen into rotation via a belt. In another variant of the drive the disc platen itself is constructed as a drive motor. This results in the most suitable drive both spatially and economically.
In a further embodiment of the invention the pressure device comprises a spring-loaded pressure disc whose diameter does not exceed the diameter of the information-free area of the storage disc. This dimensioning provides adequate pressure and leaves room for the operation of the optical unit.
In a further embodiment of the invention the storage disc, in its peripheral area, is pressed more strongly against the disc platen, whose outer edge projects slightly, the pressure device pressing the central area of the storage disc into the hollow space in such a manner that in its center the storage disc is bent into the hollow space of the disc platen in an approximately conical fashion. This flexure promotes the frictional engagement between the storage disc and the disc platen, as a result of which the storage disc is supported additionally at its periphery. The frictional engagement can also be improved by a rubber coating on the disc platen.
In conjunction with the disc flexure, the read and/or write unit, in a further embodiment of the invention, is guided along a curved guide member adapted to the flexure of the storage disc. The preload of the storage disc and the adapted guide member of the optical unit provide very exact operating conditions.
In a further embodiment of the invention the read and/or write unit with the pressure device, on the one hand, and the disc platen, on the other hand, can be moved apart. For this purpose, the disc platen is preferably movable in the height direction . This provides a simple possibility of changing a disc without much space being required.
In a further embodiment centering means serve for exactly bringing together the read and/or write unit with the pressure device, on the one hand, and the disc platen, on the other hand. In a further embodiment of the invention the centering means comprise wedges or cones on one of the apparatus sections, which face and cooperate with V-shaped or conical grooves, which are open at their upper sides, in the other apparatus section.